Method of making dichloroacetic acid



Patented Aug. 8, 1933 '7 I r e i Q i v UNITED STATES PATENT; OFFICE I Forest 0. Amstutz, Midland, Mich assignor to V The Dow Chemical Company, Midland, Mich, a Corporation of Michigan I N Drawing. Application September 4, 1 930 Serial N0. 479,787

12 Claims. (creep-'11s) The present invention relates to the manutains practically equivalent amounts of the difacture of chloroacetic acids and more particuchloroand trichloroacids and a very small larly of dichloroacetic acid. amount of the monochloro-acid, while unre- At the present time, dichloroacetic acid is acted acetic acid is entirely absent. I have usually obtained as a by-product from processes further found that such a mixture of dichloro- 60 for the manufacture of monochloroacetic acid, acetic and trichloroacetic acids may be readily as, for instance, by chlorinating hot glacial separated by converting the trichloroacetic acid acetic acid in the presence of iodine, sulphur to chloroform and carbon dioxide, the dichlorochloride, sulphur, phosphorus or other chlorine aceticacid meanwhilebeing substantially unrecarrier or catalyst. After crystallizing out monacted. vBy diluting the above mixture with water 65 ochloroacetic acid from the above mentioned and then heating at a temperature not to exchlorinated acid mixture, the mother liquor resceed 100 C. for twenty-four to forty-eight idue, which is usually made up of 40=t0 50 hours, the trichloroacetic acid is' completely per cent of dissolved monocholoroacetic acid, hydrolyzed. The chloroform and carbon dioxto per cent of dichloroacetic acid and the ide thus. obtained may be conveniently passed remainder largely a mixtureof acetic acid and through a condenser and the former compound trichloroacetic acid in varying proportions, prorecovered, if desired. vides a convenient source for obtaining dichloro- The residue from the above step, 7 consisting acetic acid. But the usual methods for sepasubstantially of amixture of water, dichloro- 20 rating mixtures of this type have proven unacetic acid and small amounts of monochlorosatisfactory because, apparently, of the: close acetic acid, is now cooled and extracted with an proximity of the boiling points and the relative organic solvent such as ether, which forms an instability of the several components thereof immiscible layer, and is separated from the when such mixture is heated or otherwise aqueous solution in the usual way. This ether 5 treated. The recovery of dichloroacetic acid layer, which contains most of the dichoroacetic from the chlorinated 1iquor, by present-methods, acid dissolved therein, is now distilled first to rarely exceeds fifteen per cent of that theoretremove the ether and upon further distillation ically possible; The dichloroacetic acid thus thefraction boiling between 190 and 195 C. recoveredalso'is of low purity. 7 consists of dichloroacetic acid'of to 95 per 3Q The present improved method has as its ob cent of purity. The recovery of dichloroacetic 5 ject the obtaining of a satisfactory yield of diacid from the above mentioned aqueous solution chloroacetic acid of high purity from the abovthereof, from which said acid is extracted with mentioned mother liquor from the manufacture ether, is generally' between 60 and. 75'per cent of monochloroacetic acid. To the accomplishof the theoretical) v 35 ment of the foregoing and related ends, the in- As extractingliquids other solvent materials vention, then, consists of the method herein-,- than ether may be employed; However, the after fully described and particularly pointed dichloroacetic acid extracted with the latter out in the claims, the following description set.- solvent contains less moisture and is therefore 7 tingforth in detail one mode of carrying out preferable to-use. Other solvents such as ethyl 40 the invention, such disclosed mode illustrating, acetate, isopropyl acetate, butyl acetate, 'isohowever, but one of several ways in which the propyl ether, etc. ormixtures of the same may principle of the invention may be used. Y be advantageously employed also for the 'pur- As previously indicated, in carrying out my pose.- In'general the solvents useful for the invention I may use a chlorinated acetic acid purpose are included in the .group consisting 45 mother'liquor from which monochloroacetic acid of aliphatic, ethers and esters. The presence 160 has been crystallized. This mother'liquor, alof small. amounts of alcohol or other similarthough the monochloroacetic acid had been impurities in the ether or equivalent solvent crystallized therefrom at a low temperature, amgiears to have no detrimental effect upon its still contains a great amount of. that constituuse as an extracting means for separating di-,

, 5o ent and may also contain a considerable quantity chloroacetic acid in the present process.

of the chlorine carrier. I have found that by A'glass or enamel ware apparatus is preferfurther chlorinating this mother liquor at a temable for carrying out the chlorinating step of perature between approximately and-190? my process. The heating or cooling therein of C., until a specific, gravity. of, about 1.58 is theliquors, etc, maybe accomplished by coils 55 reached, it is converted to. a mixture which conof similanmaterialsor otherwise. In the steps, 110

however, wherein lower temperatures are employed, the reaction vessels may be of a ceramic material, or even non-ferrous alloys or metals may be found advantageous to use.

The following example illustrates a preferred mode of carrying out my invention:-

50 pounds of chloroacetic acid mother liquor of composition approximately 40 per cent monochloroacetic acid, 50 per cent dichloroacetic acid, 9 per cent acetic acid and one per cent sulphur chloride, was introduced into an enamel lined chlorinator and heated to a temperature of from 160 tol C. with the introduction of chlorine until a specific gravity of about 1.57 to 1.58 was reached. At this point the composition of the chlorinated mother liquor by analysis was approximately 10 per cent monochloroacetic acid, 50 per cent dichloroacetic acid, and 40 per cent trichloroacetic acid. This chlorinated mother liquor was now transferred to a vessel similar to that used above and equipped with a condenser, diluted with water to about four times 'its original volume and the temperature thereof maintained at between 35 and C. for forty-eight hours, when a test of the diluted mother liquor by the familiar carbylamine reaction test for trichloroacetic showed the complete absence thereof. Dichloroacetic acid and m'onochloroacetic acid were found to be present in the diluted mother liquor in the ratio of approximately 9 to 1. This diluted mother liquor was then well cooled and extracted twice with ether, using 10 pounds for each extraction. The combined ether extracts contained approximately per cent of the dichloroacetic acid present in the diluted mother liquor. Upon redistilling, the fraction between 190 and 196 C. consisted of a dichloroacetic acid product approximately 91 per cent pure, the remainder being mostly monochloroacetic q 'tures between approximately 140 and 190? C.

acid. The yield of dichloroacetic acid amounted to 72 percent of the quantity thereof contained in the original mother liquor.

The point at which the chlorination of the acetic acid mother liquor is preferably stopped, e. g. at specific gravity 1.58, at temperatures between about 140 and 190 C., represents the approximate point at which the ratio of dichloroacetic acid to the monoand tri chloroacetio acids therein is at a maximum. These percentages of the three. acids are substantially those stated above in the example. It is evident that this gravity may vary somewhat if larger amounts of impurities are present or if the'composition of the original mother liquor is otherwise changed. That substantially favorable ratics of the mono-, diand tri-chloroacetic acids in the chlorinated acetic acid mother liquor may be obtained at gravity points somewhat higher or. lower than that specified, is also evident.

In the foregoing special reference has been made by way. of illustration to the use of the chlorinated mother liquor from the monochloroacetic acid process ,as av raw material for carrying out my-improved process for making dichloroacetic acid. It is understood that I do not so .limit myself, but includeas well other convenient and adaptable materials or mixtiues of compounds that may be suited to such use. It is also understood that I may chlorinate acetic acid or a solution containing acetic acid 7 to form a mixture consisting substantially of dichloroacetic andtrichloroacetic acids without introducing an intermediate step for the removal of monochloroacetic acid, and then separate the dichloroacetic acid as hereinbefore described.

Other modes of applying the principle ofmy invention may be employed instead of the one explained; change being made as regards the method herein disclosed, "provided the steps stated by any of the following claims or the equivalent of such steps be employed.

I therefore particularly point out and distinctly claim as my invention:-

1. Ina method of making dichloroacetic acid, the steps which consist in reacting acetic acid with chlorine to form a mixture consisting chiefly of dichloroacetic and trichloroacetic acids, hydrolyzing the latter by heating with water,expolling the products of hydrolysis therefrom, and extracting the dichloroacetic acid from the resultant aqueoussolution with a solvent immiscible with water.

2. In a method of making dichloroacetic acid, the steps which consist in reacting acetic. acid with chlorine" to form a mixture consisting chief ly of dichloroacetic and trichloroacetic acids, hydrolyzing the latter byheating with water, expelling the products of hydrolysis therefrom, and extracting the dichloroacetic acid from the resultant aqueous solution with a solvent included in the group consisting of the aliphatic ethers and esters. i

3. In a method of making dichloroacetic acid, the steps which consist in reacting acetic acid with chlorine to form a mixture consisting chiefly of dichloroacetic and trichloroacetic acids, hydrolyzing the latter by heating with Water, expeliing the products of hydrolysis therefrom, and extracting the dichloroacetic acid from the resultant aqueous solution with ethyl ether.

4. The method of making dichloroacetic acid which comprises reacting a chlorinated acetic acid mother liquor with chlorine at temperato convert the monochloroacetic acid thereof substantially to dichloroacetic and trichloroacetic acids, diluting said mother liquor with water, heating the resultant aqueous mother liquor solution at atemperature not to exceed '100'.' C..

temperature between approximately 140 and 190 C. to form a mixture consisting substantiallyof dichloroacetic and trichloroacetic acids, diluting said acid mixture with water, heating the resultant aqueous acid mixture at a temperature not to exceed C. to hydrolyze the tri-.

chloroacetic acid thereof substantially to chloroform and carbon. dioxide and toremove the latter two substances, cooling the residue remaining and extracting the dichloroacetic acid therefrom with a solvent immiscible with water.

140 and 190 C.ito form a mixture consisting substantially of dichloroacetic and 'trichloroace tic acids, dilutingthe resultant acidmixtur'e with water, heating the resultant aqueous acid I mixture at a temperature not to exceed 100 C.

to hydrolyze the trichloroacetic acid thereof to form substantially chloroform and carbon dioxide and to remove the latter two substances, cooling the residue remaining and extracting with ethyl ether and, distilling the ethyl ether extract to recover dichloroacetic acid therefrom. 7. The method of making dichloroacetic acid which comprises chlorinatingv acetic acid at a temperature from about 140 to 190 C. until a specific gravity of approximately 1. 57 to 1.58 is reached, heating the mixture with water at a reaction temperature not to exceed 100 C. to hydrolyze trichloroacetic acid, and separating dichloroacetic acid from the residual mixture.

8. The method of making dichloroacetic acid which comprises chlorinating acetic acid at a temperature fromabout 140 to 190 C.'until a specific gravity of approximately 1.57 to 1.58 is reached, diluting with water, heating the aqueous solution at a temperature not to exceed 100 C. to hydrolyze the trichloroacetic acid contained therein substantially to chloroform and carbon dioxide and to remove the latter two substances, cooling the residual aqueous solution, extracting with ethyl ether, and distilling the ethyl ether extract to recover the dichloroacetic acid therefrom.

9. The method of making dichloroacetic acid which comprises chlorinating a monochloroacetic acid mother liquor at a temperature from about 140 to 190 C. until a specific gravity of approximately 1.57 to 1.58 is reached, heating the mixture with water at a reaction temperature not to exceed 100 C. to hydrolyze trichloroacetic acid, and separating dichloroacetic acid from the residual mixture;

10. The method of making dichloroacetic acid which comprises chlorinating: monochloroacetic acid mother liquor at a temperature from about 140 to 190 C. until a specific gravity of ap-' proximately-1.57 to 1.581s reached, diluting with water, heating the aqueous solution at a temperature not to exceed 100 Cato hydrolyze the trichloracetic acid contained therein substantially to chloroform and carbon dioxide and to remove the latter two substances, cooling the residual aqueous solution, extracting with ethyl ether, and distilling the ethyl ether extract to recover the dichloroacetic acid therefrom.

11. The method of recovering dichloroacetic trichloroacetic acid is hydrolyzed and dichloroacetic acid remains substantially unreacted.

FOREST 0. AMST'UTZ. 

